Production of synthetic elastomers



March 29 w49 w. F. FARAGHER Erm.

PRODUCTION 0F SYNTHETIC ELASTOMERS 3 Sheets-Smet v1 Filed Nov. 8, 1943 Y Nu QR` K gu m.

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INVENTR n/.FFnRAo//ER JJM #AKR/50N ATTORNEY Marcl'lzg, 1949. w, F, FARAGHER -Er AL '2,465,363

PRODUCTION 0F SYNTHETIC ELAsToMERs 5 SheetsSheej. 2

Filed Nov. 8, 1943 INVENTOR PV. E FARAGHER JJM HARK/50N WMM ATTORNEY Patented Mar. 29, 1949 Masas PRODUCTION F SYNTHETIC ELASTOMEBS Warren F. Faragher, Swarthmore, Pa., and James W. Harrison, Woodbury, N. J., assignors to Houdry Process Corporation, Wilmington, Del., a corporation of Delaware Application November 8, 1943, Serial No. 509,431

4 Claims.

The present invention relates to improvements in catalytic polymerization and has particular reference to new and improved methods for the production of synthetic rubber which result in I' a characteristically new typeof synthetic rubber.

Initially., attempts were made to duplicate natural rubber in both physical and chemical characteristics. This attempt at duplication was dropped in favor of the production of materials differing chemically from natural rubber, but havingto some extent the physical characteristics thereof. Initially, the most important pro cesses were based on a single phase reaction employing sodium as a catalyst. In this work there was, of course, no water present since the sodium would reactviolently therewith. In the early 1920's, development of the modern method of polymerization to synthetic rubber started and involved polymerization of diolens in a water emulsion.

Present commercial processes are disadvantageous in several respects. In the rst place, the polymerization requires a. reaction ,time on the order of ilfteen hours. Secondly, 'the crepe produced has poor milling characteristics. Further, it should be noted that the reactors, operating under the conditions known in the art and in present commercial use, are of stainless steel or of glass lined materials. This entails a very substantial investment cost for a plant of commercial size.

The reaction time could be reduced considerably by running at a higher temperature. When it is attempted to increase the temperature of a batch autoclave in order to reduce the reaction time the physical properties of the rubber produced become progressively lower up to approximately 80 C., above which there is a sharp and very `marked decrease in physical properties. Fig. 4 of the drawing illustrates this degeneration of the physical properties of the rubber produced in a batch autoclave at varying reaction temperature. 'This gure is a group of graphs showing the effectoftemperatures from 40 to 93 C. on

tensile strength, on percent elongation of the rubber produced, and on reaction time,- the reaction time being selected to give the maximum tensile strength under the conditions of operation. The reaction mixture was the conventional parts butadiene and 25 parts styrene, 200 parts water, 5 parts soap, .3 part potassium persulfate and .6 part dodecylmercaptan, each by weight. When the temperature was raised from 40 to 2 The elongation was substantially constant at between 500-and 600%, whereas the time dropped from 22 hours to .one and three-quarters hours. By increasing the temperature to 93 C., however,

the maximum tensile was obtained in only threequarters of an hour. However, the tensile was only 1620 and the elongation dropped to 245%.

- For this reason elevated temperatures have not been used for the production of synthetic rubber, though temperatures up to about C.'have been mentioned in the patent literature on `:mulsion polymerization. f y

Objects of the present invention are to provide improved processes for the production of synthetic latex in short reaction time which avoid detrimental eiect on the physical propertiesr of the cured rubber, to provide processes for the production of synthetic latex of substantially improved milling properties, and to provide processes for the production of synthetic rubber which allow the employment of ordinary carbon steel for the reactor. vantages will be apparent as the description proceeds.I

y'I'he present invention is of particular application to high temperature polymerization of conjugated dioleiln emulsionsto latex in a tubular reaction zone. In accordance with the present invention the deposition of polymer in the zone is prevented by agitation effected by ow of the emulsion in the zone.

In the accompanying drawings Figs. 1 to 3 are flow sheets of different systems embodying the present invention, while Fig. 4 is acomposite graph of the eilectv of temperature variations from 40 to 93 C. upon time of reaction and physical properties of rubber produced. wAny conjugated diolefln may be employed in the present processes, including, for instance, butadiene itself or any suitable butadiene derivative, such` asisoprene, 2-3 dimethyl butadiene or Y 1-methyl butadiene.

Other unsaturated materials may be copolymerized with the conjugated diolefin to produce rubber, for example compounds having a styrene nucleus., such as styrene, a-methyl styrene, ortho.

meta, or para-methyl styrene, a-para dimethyl styrene, or ortho-para dimethyl styrene. These and other unsaturated materials copolymerizable with butadiene to latex are well known in the art and have frequently been discussed in the literature.

The polymerization reaction is conducted in an aqueous emulsion. Any suitable emulsifying 80 C. the tensile dropped off fromI 3000 to 2250.` lili4 agent may be employed, such as soap or a suitable Other objects and ad-l :Massa I pose may be employed, such as fatty alcohol or acid sulfates or sulfonates, such as lauryl sulfate or sulfonate, the sulfate or sulfonate of Iauric acid, and alkylated napthalene sulfonic acids, and salts of higher fatty amines. Optionally, an emulsion stabilizer may be added such as glue, agar agar or starch. Likewise, for stabilization. one may Withdraw emulsion from the reactor before reaction, after partial reaction, or after polymerization is complete, and introduce it into the materials to be emulsiiled.

The polymerization is conducted in the presence of a catalyst. Any of the well-known catalysts for polymerizing butadiene emulsions to latex may be employedf,4 as for example, alkali metal and alkali earth metal peroxides, perborates or persulfates, diazo amino benzene, ,benzoyl peroxide, gasoline peroxide and silver oxide. Other materials which have now been found uselul in the polymerization of butadiene emulsions to latex are nickel carbonyl and tetraethyl lead. As is well known, the catalytic polymerization may be conducted in the presence of a modiiler suchas dodecylmercaptan. It should be noted that, under the high temperature reaction conditions of the present invention, the percent of modier for the most desirable effect may be reduced from about 1% to not over about 0.5%.

The emulsiiled dioleiln, together with the catalyst, is fed to a tubular reaction zone. The temperature'ot the reactants in the tubular reaction -zone is preferably controlled by indirect heat exchange with any suitable medium circulating outside of the reactor, such as oil. The polymerization is eilected at a temperature between 100 and 175 C. Suillcient pressure is employed to maintain the reactants substantially in liquid phase. In this temperature range a latex is obtained having excellent milling characteristics.

In accordance with the present invention we prevent the deposition of polymers upon the inner surface of the reactor wall by agitation of the emulsion within the zone effected by flow oi the emulsion. When agitation is effected by ilow of emulsion in the reaction zone one may either flow the emulsion in one direction through the tube or produce a reciprocating ilow. With unidirectional ilow the process is normally run continuously, though it may be employed for a batch operation by introducing the emulsion into an endless tubular reactor and pumping it in one direction through the reactor. With the reciprocating type of ilow the process may be either continuous or batchwise.' Thus, for a non-continuous process using reciprocating ilow the emulsion is introduced into the tube under pressure and portions are then alternately introduced and withdrawn at opposite ends of the reactor. For a continuous process using reciprocating flow the withdrawal and introduction of the solution near the ends of the tube are the same, but iresh charge is continuously fed into the inlet and reaction products 1 continuously withdrawn from the outlet of the zone.

If desired, organic solventsmay also be em ployed to supplement agitation by flow for the I prevention of deposition of polymers within the' reaction tube. The solvents which may be employed include aliphatic hydrocarbons ofy from 3 to 12- carbon atoms or higher. -Preferred solvents, in accordance with the present invention,

are aromatic solvents such as benzene. toluene, xylene, ethyl benzene cumene, methyl cumene and the like. The action of the solvents may be connected with the property of swelling the higher polymers inasmuch as complete solubility of these polymers in the solvent is unnecessary in order to prevent deposition 'within the reactor.

The volumetric ratio of the aqueous phase of the emulsion to the hydrocarbon phase thereof may vary considerably and is not critical in the 4broad -aspect of this invention. As indicative ci V4the range of operation, one may employ a ratio in the range of 0.4 to 3. The amount of soap employed, preferably, is in the range of between 2.5%

Vand '1.5% t

` tion formed forwardedto soap storage tank 0.

'dIhe ,soap employed may either be all fresh soap or be, in part, soap reclaimed from the process. Water and the desired catalyst are introduced into the mixing tank ,1.1 The aqueous soap solul tion and aqueous catalyst solution or suspension are then forwarded by lines l and I, respectively,

g to the mixing zonelll, wherein they are thorough'- ly intermixed. Inhibited butadiene is withdrawn from storage tank I land introduced into distillation column i2 wherein it is stripped of inhibitor. Butadiene withdrawnoverhead from the distillation column I2 is introduced into condenser il,

' a-'methyl styrenein line i6 are introduced into mixing zone i1.

The aqueous charge in mixing zone I0 and the oil charge in mixing zone I 1 are withdrawn by lines I8 and Il, respectively. and are introduced Vinto an emulsifying zone 20 by pumps 2l and 22, respectively. Any suitable emulsiiler may be employed. Preferably a continuous emulsiiler is used. Suitableemulsitlers, for instance, are the vibrating valve type of emulsiiler and the perforated plate type in which the mixture to be emulsifled is passed through a series of plates having small diameter perforations therethrough.v The emulsion so formed is introduced into reactor 23 having a'reaction zone of tubular shape. Thus. in the reactor shown a continuous tube is employed. The reactor 23 is provided with a jacket containing a suitable heat transfer iluid. such as oil,l which circulates in either direction through the reactor 2 3, heat exchanger 24 and pump 25. The reactor tube is of length sumcient that agitation is c iected by ilow of emulsion through the tube. The solvent supplements the agitation in preventing deposition of polymers within the tube, The violence of agitation may .be controlled by increasing the length of the tube with the same through-put or by increasing the through-put with the same length of tube.A Emuent latex from the reactor 23 is passed to ilash tank 26 through heat hexchanger 21, in which the` Butaqlene which a flashed Orrin ,tank is a l forwarded by line 2O to a recovery system com' prising an acid scrubbing zone 'I l, to remove any soap solution Vcarried over, provided with an acid recirculating pump 32. Butadiene from.,

zone Il is forwarded to a'liguid' trap ll and then to water washing zone 34 to remove acid from accusa the gas. The butadiene so purified is theny ref cycled into the' condenser I4 by line-38. The effluent latex from flash tank 2l may be'handled in any desired or conventional manner. As shown in Fig. l, it is introduced into a ste'ain distillation zone 36 operating under vacuum. through pressure regulating valve 31. When the arated by distillation prior to coagulation'it is of utility to add an antifoaming agent in order' to minimize carry-over of the synthesized polymer. The aromatic oil vapor, together with steam, is forwarded byline 33 for recovery. Residual latex is then introduced alternately into :tanks 39 and 40 through valved lines, onetank' being under vacuum and being filled, while the vacuum' on the other tank is broken, and the tank is being discharged through a valved line to the coagulation zone 4l. Conventional'methods vmay be employed for coagulation, such as the addition of salt to the latex and bubbling of.carbon dioxide therethrough. After coagulation the mixture is filtered in illtration zone 42. The coagulated latex may then be '.:ashedn in zone 43 with acid; The filtrate from zone 42 and the wash water from zone 43 may then bel sent'for soap reclaiming at 44 and the reclaimed soap returned to mixing tank 5' through line'l.

After separation of soap from the latexl by theacid washing vthe coagulated latex may then bev further steam-distilled in zone 46 to remove aro-v matic oil from .the'latex which is then' ready for nishing as crepe.

The steam distillates from zones 36 and '46 are condensed and then decanted in zone 41 to' Fresh cumene is introduced. by line 50 into a-4 dehydrogenatio zone for'the preparation of af methyl styrene therefrom. This dehydrogenation which is conducted in zone 5| is preferably run at low temperature in the presence of an active dehydrogenation catalyst. It has been found that unexpectedly good results with respect to the physical properties of rubber may be 'obtained when the cumene is dehydrogenated in this-manner. The effluent from zone 5| is introduced into zone 48 in indirect heat exchange relation withrecycle aromatic oil and then into tower or flash tank 52 to remove hydrogen over` head. The two streams of cumene and v'rz-methyl styrene are then introduced linto distillation column 49, wherein a rough cut distillationf'is made to separate some of the cumene as an verhead, which is recycled through line 53ior ine-"j troducti'inwinto the dehydrogenation zone. The, bottoms containing a mixture of cumene. and:

a-lnethyl styrene in the proportion desired is forwarded by line I B to mixing zone I1.

'I'he specific system Aabove described is of utility in any instance in which pairs are desired such as ethyl benzene and styrene or p methyl styrene and p'methy1ethylbenzene.

Fig; 2 shows a form of the invention in which deposition of the polymers in the reaction zone is prevented by agitation produced by reciprocating flow of the emulsion in the reaction zone.

YYYaromatic oil contained in the latex is thus seD'-" Butadiene and styrene are fed to the system through line l0 and 6| vand are introduced into mixing zone I1. 'I'here are also introduced into mixing zone I1 by line 62, the benzene employed .for solvent and any recycle styrene. vThe oil mixture from zone I1 is fed to the reaction zone 64 by pump 22. The soap and catalyst solution.

which may be prepared as shown in Fig. 1, is fed likewise to the reaction zone by pump 2l.

As shown in Fig. 2, the reaction zone 64 -is tubular. the reactants being fed at one end of.

the tubular zone and withdrawn at the other. There is provided a valveless pump 65, opposite ends of which are connected to the opposite ends of the reaction zone. By this means when the piston moves in one direction emulsion is withdrawn from the inlet end of the tube and emulsion previously withdrawn from the outlet end is reintroduced thereinto. When the piston moves in the opposite'direction that material withdrawn from'the inlet is reintroduced thereinto and equal amount withdrawn from the outlet. Thus reactants at opposite ends of the reactionzone are notjcommingled but are maintained separate. When the reaction zone is -sb operated n'o separate emulsifler need be employed as theinlet end of the'reaction zone, including' the cooperating section of the pump, functionsl as an emiilsiiiex".y

As in Fig. 1 polymerized latex is withdrawn from the outlet of the reaction zone through heat exchanger 21 to pressure regulating valve 28, to

y lflash tank 26 from which impure butadiene is withdrawn for purification and recirculation.

The latex may then' be withdrawn through presfilter 42, the wash waters from 43, and the steam distillate from 46 are then introduced into a decantation zone 41. In case the overhead from z one 41 is substantiallyIv free of butadiene dimer, this overhead may be passed directly to mixing zone i1 by line 62.

Fig. 3 shows a system in which unidirectional flow in a cyclic system is employed to eifect agitation' by flow in a relatively short reaction zone.

In this system butadiene, a-methyl styrene andl recycled aromatic oill are introduced into mixing zone I1. The soap and catalyst solution and the oil mixture are introduced into reaction zone "through an emulsiiication zone 20. The reaction zone 10 is of tubular shape and is provided with indlrect heat exchange temperature control, as in Fig. 1. The reaction zone 10, as shown, is an endless tubular zone provided with a pump 1I operating in a single direction. Thus. a reciprocating pump may be employed of the conventional type having valves so that the flow islnotreciprocating but'is unidirectional through the pump. Accordingly, rfresh reactants 'are continuously introduced into reaction zone at one point and reaction mixture is withdrawnat another point to the pressure regulating Valve 28 and introduced into the flash tank 26, from which butadiene is withdrawn for re-circulation, preferably through a purification system, as shown in Fig. 1. The latex is then coagulatedat 4|, filtered at 42, washed at 43 and steam distilled at 46. The aromatic oil from the filtrate, wash water. and steam distillate may be recovered by sensesing was omitted and the similar rest period bel:

tween curing and resting was cut to 30 minutes. While the physical constants of tensile strength and elongation are not as high usingthis rapid method as under the A. S. T. M. method, indicative results are obtainable, there being a good. correlation between the two. v

Example 1 A mixture of 60 parts butadiene, 40 partsY styrene was emulsifled in a soap solution, the volume ratio of soap solution to hydrocarbons being equal to 1.4, and the soap solution containing 7.5 parts of soap. There was also added 0.25 part of potassium persulfate and 0.3 part of dodecylmercaptan. This emulsion was fed continuously to a tubular reaction zone in which reciprocating iiow was employed to effectA agita,- tion. The temperature in the .reactor tube was maintained at about 107 C. and the emulsion was :fed at a rate to give a reaction time of thirty minutes. A 78% conversion was obtained to latex which upon test had a modulus at 300% of 1560, a tensile of 2360 and an ultimate elongation of 440.

simple z A hydrocarbon mixture of 52.5 parts of butadiene, 17.5 parts styrene and parts benzene, each by weight, was prepared. The'butadiene to styrene ratio was 75:25. This hydrocarbon mixture was emulsied with 1.4 volumes di soap solution per volume of hydrocarbons (2.0 weight ratio of water to hydrocarbon), the soap solution containing 5 parts by weight of soap, 0.25 part potassium persulfate and 0.3 part dodecylmercaptan. The emulsion was passed through a reaction tube controlled to a temperature of 135 C, under a pressure of 600 lbs. per square inch.' The time of contact was 30 minutes. Agitation within the reaction zone was attained by reciprocating ilow within the tube at an average linear rate of seven feet per second, reactants being continuously introduced and withdrawn from the tube. A 71.1% conversion to synthetic rubber was obtained, which upon curing. had a modulus at 300% of 1400, a tensile strength of 1620, an elongation of 325 and a set of 10.

Example 3 Example 4 '70 at 300% oi.' 1580, a tensile of 87` l' asetoi27. A.B.T.M.testsshowedamodulus of 465 andaset ot 37.

Iaample 5 1Example 4 was repeated atl a temperature o! 112 C. at a 40 minute time oi contact. A 72%- conversion to synthetic rubber was obtained, which upon testing. had a `modulus at 300% of 1080, a tensile of 2870, an elongation of 810 and a set of 39.

w Example I v Example 3 was repeated with tbe exception that only half of the butadiene was fed at the inlet of a reaction tube together with all oi tbe styrene. One-third of the way along the reaction tube V4 of the butadiene was fed and the remaining V4 of the butadiene was fed at a point twov thirds the way along the tube. A conversion was obtained, which upon test, showed a modulus of i265, a tensile of 2480, an elongation of 535 and a. set of 29. The procedure was further conversion to synthetic rubber was obtained;

which upon test, showed amodulus at 300% of 1095, a tensile o f 2415, an elongation of 620. and a set of 59.

' lmmple 7 u A hydrocarbon mixture wasprepared contain. ing 42 parts butadiene, parte of styrene and 30 parts benzene by weight; This was fed through a reaction tube emulsified in a soap solution equal in volume to 0.7 the volume of the hydrocarbon mixture, which soap solution contained 7 parts of soap, 0.25 part ot potassium persulfate and 0.3 part of dodecylmercaptan. each by weight. Agitation was effected by iiow ot the emulsion in a tubular zone, as in Example i. The reactants were fed at a rate to give a time ot contact of 28 minutes and the temperature was maintained at 107 C. A 66% conversion was obtained to a rubber having a modulus at 300% ot 1320, a tensile of 2020 and an elongation of 525.

Example 8 Cumene was dehydrogenated at a temperature in the range of 1000 to 1100 F. in contact with a chromium oxide alumina dehydrogenation catalyst. Hydrogen was separated from the reaction mixture whereby a ,mixture was obtained containing a-methyl styrene and cumene. A weight of butadiene equal to the a-methyl styrene was added to tbe a-methyl styrcnecumene mixture. Enough benzene was addedto bring up the total of benzene and cumene to equal 30% oi the total hydrocarbon mixture. This mixture was emulsiiied with 1.4 volumes of soap solution per volume of hydrocarbons. The soap solution contained 5 parts of soap. constituted of sodium oleate and sodium stearato, per parts of hydrocarbon, and 0.25 part of potassium persulfate and 0.3 ot dodecylmercaptan per 100 parts of reactants. After a 50 minute time ot contact in a tubular reaction zone maintainedat C. and at 600 lbs. per square inch in which reciprocating iiow was etl'ected, as in Example i, a 68.5% conversion to synthetic latex was obtained, which when processed had a modulus at 300% of` 1200, a tensile of 2115. an elongation of 500 and a set of 35.

2580, an elongation Example 9 Example 8 was repeated at a temperature of 113 C. and at a 57 minute time or contact. A

Example 10 A mixture was prepared of 21 parts of butadiene, 21 parts ot isoprene,'28 parts ot styrene and 30 parts of solvent constituted of saturated C5 hydrocarbons and benzene. each by weight. This was emulsied with 1.4 volumes of soap solution per volume of hydrocarbons, which soap solution contained 7.5% soap based on total hydrocarbons and 0.25% potassium pei-sulfate and 0.30 dodecylmercaptan, based on reactant hydrocarbons only. The emulsion was conducted through a continuous reaction tube at a temperature of 110 C., at a rate to give a time of contact in the tube of 55 minutes, with agitation as in Example 1. A 64.5% conversion to synthetic rubber was attained, which upon test, gave a modulus at 300% of 1195, a tensile of 2400, an elongation of 565 and a set of 40. A. S. T. M. tests gave a modulus at 300% of 1150, a tensile of 2510, an elongation of 535 and a set of 39.

3. The process ot preparing synthetic elastomers which comprises copolymerizingin a tubular reaction4 zone a conjugated diolen hydrocarbon` of from 4 to 6 carbon atoms and a styrene compound i'rom' the group consisting of: styrene, a-methyl styrene, o-. mf, and p-methyl styrencs. a-p-dimethyl styrene, and o-p-dimethyl styrene; said conjugated diolefin and said styrene compound being contained in an aqueous emulsion including a mono-nuclear'aromatic hydrocarbon free from side chain unsaturates and which is liquid at the recited reaction temperature, maintaining the temperature of the emulsion in-said reaction zone during polymerizing at above 100 C. and below 175 C., and agitating the emulsion within the reaction zone by reciprocating vilowoi.' the emulsion, thereby preventing deposi- Each of the runs in the above examples was conducted in tubular reactors provided with indirect heat exchange to control the temperature as indicated. In none of these runs was there any deposition of polymer within the tube. While these reactor tubes were fabricated of common. carbon steel, no corrosion occurred as a result of these and other runs made under the conditions of the present invention.

We claim as our invention:

1. The process of rubber manufacture which comprises polymerizing a conjugated dioleiin having 4 to 6 carbon atoms in aqueous emulsion in a tubular reaction zone, maintaining the temperature of said zone above 100 C. and below 175 C. and preventing the deposition of polymer on the walls of said reaction zone by agitation eiected by reciprocating flow of the emulsion in the tubular zone.

2. The process of rubber manufacture which comprises copolymerizing conjugated butadiene and styrene in aqueous emulsion in a tubular reaction zone, continuously introducing reactants t at one end of the zone and continuously withdrawing reactants from the other end of the zone, maintaining the temperature of said zone above 100 C. and below 175 C. during polymerizing, the aqueous phase of said emulsion containing between 2.5 and 7.5% of soap based on total hydrocarbons and eiIecting agitation of the emulsion in the zone by reciprocating flow o! the emulsion ln the zone.

tion of polymeric materials in the reaction zone.

l REFERENCES errar) The following references are of record in th le of this patent:

Number Name Date 1,898,522 Bock Feb. 21. 1933 40 1,910,847 Maximo May 23, 1933 I 1,973,000 Konrad Sept. 11, 1934 2,097,263 Strain Oct. 26, 1937 2,161,481 Marks June 6, 1939 2,234,204 Starkweather Mar. 11, 1941 2,259,180 Schoenfeld Oct. 14, 1941 2,334,195 Hopf! Nov. 16, 1943 I 2,384,277 Calcott et a1. Sept. 4. 1945 FOREIGN PATENTS Number Country Date 312,201 Great Britain May 21, 1929 318,115 Great Britain Aug. 26, 1929 517,951 Great Britain Feb. 13, 1940 .518,657 Great Britain. Mai. 4. 1940 671,272 France Mar. 16, 1928 UNITED STATES PATENTS OTHER REFERENCES A. Talalay & M. Magat. Synthetic Rubber from .lohoh Interscience Publishers, Inc. 1945, page n Certicate of Correction l Patent No. 2,465,363. March 29, 1949.

WARREN F. FARAGHER ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows:

Column 7, line 33, for the numeral 2360 read 2680;

and that the said Letters Pat-ent should be read with this correction therein that the same may conform to the record of the case in the Patent Ofce.

Signed and sealed this 20th ldey of September,`A. D. 1949.

JOE E. DANIELS, V

Assistant Uommiaat'ovwr of Patente. 

